Saturday, August 15, 2015

Global Warming and the Pacific: Kevin Trenberth's Perspective

Earlier today, Anthony Watts copied and pasted a press release about a new article from Kevin Trenberth (archived here). Anthony, who didn't even link to the press release, complained he couldn't find the article and asked his readers to tell him where it was. Did he really want that? Or did he just pull out that press release because, for a change, he recognised the name and figured it was sure to rouse the lynch mob? Anthony wrote:

From the AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE and the “if warming can’t overcome Nature, is it really there at all?” department.

It's another case of Anthony not reading or not understanding what he copies and pastes. (And that he favours bureaucracy - with his "department", which is a new gimmick he's introduced just recently, and getting old already.) The press release was short, and down the bottom was this:

Article #7: “Has there been a hiatus?,” by K.E. Trenberth at National Center for Atmospheric Research in Boulder, CO.

Here's a free tip. If you see the title and the author of an article, there's a nice little search engine that came to prominence a few years back. It's very useful.

Kevin Trenberth on the ups and not so ups of global surface temperature

Dr Trenberth's article was about the big ups and lesser ups of global surface temperature. It's a Perspective article in the latest issue in Science mag. If Anthony had bothered to read the press release he posted, he might have liked what he read. Bob Tisdale might learn something from it, too, except for the fact that Bob thinks he knows more than the scientist who taught him what little he (Bob) knows. Dr Trenberth writes about how it's not just greenhouse gases that affect global mean surface temperature, there are natural climate variations as well. Here's an excerpt from the press release at EurekAlert (my paras):

...Kevin Trenberth argues that natural climate fluxes - larger than commonly appreciated - can overwhelm background warming, making plateaued rates, or hiatuses, deceiving in significance. After many years of monitoring, it's clear that the GMST can vary from year to year, even decade to decade; these differences, Trenberth argues, are largely a result of internal natural variability.

For example, the Pacific Decadal Oscillation (PDO), a phenomenon where the Pacific Ocean goes through periods of warming and cooling, can have a very strong impact on the climate by altering ocean currents, convection, and overturning. The PDO results in more sequestration of heat in the deep ocean during the negative phase of the PDO; therefore GMST tends to stagnate during this negative PDO phase, but increases during the positive phase. Indeed, observations and models show that the PDO is a key player in the two recent hiatus periods.

Some other examples of causes behind natural variation include El Niño, volcanic activity, and decreased water vapor in the stratosphere. These natural variations are strong enough to mask steady background warming at any point in time, Trenberth argues.

In the Perspective article in Science, Dr Trenberth points out that there have been slowdowns and pauses in global warming over the past century. He mentions the "big hiatus" from about 1943 to 1975, and how the stalling of temperature from 1950–1975 artificially lowers the rate of increase for the 1950–1999 period. He pointed out that latter period is what Karl et al compared the warming from 2000 to 2012 with. You might recall that Karl15 found that the rate of warming from 1950 to 1999 at 0.113°C decade−1 was statistically indistinguishable from the rate of warming from 2000 to 2014 at 0.116°C decade−1. However, when you're looking at rates of warming, it depends a lot on which periods you pick for comparisons.

Dr Trenberth wrote how natural internal variability can have quite a large effect on global surface temperature. He included a chart, showing surface temperature over time, together with phases of the Pacific Decadal Oscillation (the PDO).

A staircase of rising temperatures.(A) Seasonal (December-January-February; etc.) global mean surface temperatures since 1920 (relative to the 20th-century mean) vary considerably on interannual and decadal time scales. Data from (19). (B) Seasonal mean PDO anomalies (8) show decadal regimes (positive in pink; negative in blue) as well as short-term variability. A 20-term Gaussian filter is used in both to show decadal variations, with anomalies reflected about the end point of March to May 2015 (heavy black curves). (C) Decadal average anomalies (starting 1921 to 1930) of GMST (green) along with piecewise slopes of GMST for the phases of the PDO (orange). Note how the rise in GMST (A) coincides with the positive (pink) phase (B) of the PDO at the rate given in (C). Source: Trenberth15

While the increase in global surface temperature is caused by increasing greenhouse gases, Kevin's closing paragraph was about what causes changes in the rate of increase in the global mean surface temperature (GMST). He attributes that to the Pacific Ocean:

The main pacemaker of variability in rates of GMST increase appears to be the PDO, with aerosols likely playing a role in the earlier big hiatus. There is speculation whether the latest El Niño event and a strong switch in the sign of the PDO since early 2014 (see the figure) mean that the GMST is stepping up again. The combination of decadal variability and a trend from increasing greenhouse gases makes the GMST record more like a rising staircase than a monotonic rise. As greenhouse gas concentrations rise further, a negative decadal trend in GMST becomes less likely (13). But there will be fluctuations in rates of warming and big regional variations associated with natural variability. It is important to expect these and plan for them.

ENSO and the Pacific Decadal Oscillation

A little while ago I updated the PDO/ENSO chart. Here it is. It includes 2015 to date (almost). Click to enlarge it.

Looking at the past few years, what you can see is that in the cool phase, El Niños don't warm as much as they do in a warm phase. It does look as if the cool phase doesn't mean successive La Niñas will make things cooler though, going by what happened since 1998. I'd suggest that's because of the greenhouse effect - but I should probably check that with Dr Trenberth.

If the PDO is entering another warm phase (as indicated on the above charts), then that would probably mean the next few years could warm up rather quickly again. It's too soon to tell.

Other recent research on the last few years of surface temperature

This isn't the first paper that Dr Trenberth has written about the influence of the PDO on surface temperature. For example, back in 2013, he and John Fasullo wrote a paper in the AGU open access journal, Earth's Future, on a similar topic. From the abstract:

More than 90% of the heat goes into the oceans and, with melting land ice, causes sea level to rise. For the past decade, more than 30% of the heat has apparently penetrated below 700 m depth that is traceable to changes in surface winds mainly over the Pacific in association with a switch to a negative phase of the Pacific Decadal Oscillation (PDO) in 1999. Surface warming was much more in evidence during the 1976–1998 positive phase of the PDO, suggesting that natural decadal variability modulates the rate of change of global surface temperatures while sea-level rise is more relentless. Global warming has not stopped; it is merely manifested in different ways.

Time for Bob Tisdale to eat crow

Bob Tisdale, a denier who writes for Anthony Watts' conspiracy blog, thinks that global warming is caused by El Niño events. (Think about this for two seconds, if it takes that long. The oceans would have all evaporated by now - just one of the many objections to that silly notion.) A little while ago he even claimed that in 2009 he was the first to notice that there were shifts in surface temperature. He claimed that this was caused by strong El Niños. He's wrong on one count and partly wrong on the other. He was well and truly beaten to the punch in regard to noticing regime shifts in surface temperature following an El Niño. A Google search brings up the following for example, and they weren't the first:

Moreover, we observe step-like discontinuities both in sea level and SST by mid-1994 and early 1997 clearly related to the 1994 and 1997 ENSO events. (Cazenave et al, 1998)

The second assessment report of the IPCC, from 1995, quotes Trenberth and Hurrell (1994) in regard to "substantial changes in the North Pacific atmosphere and ocean began about 1976". And in the same section:

The Pacific decadal time-scale variations have been linked to recent changes in the frequency and intensity of El Niño versus La Niña events and it has been hypothesised that the decadal variation has its origin in the tropics (Trenberth and Hurrell, 1994).

There's an earlier paper by Kevin Trenberth, from 1990, in which he discusses interdecadal climate changes in the Northern Hemisphere. From that paper:

The North Pacific changes appear to be linked through teleconnections to tropical atmosphere—ocean interactions and the frequency of El Niño versus La Niña events.

And he specifically mentions "the different regime after 1976".

So at least 25 years ago, almost twenty years before Bob Tisdale noticed anything, Dr Trenberth was researching the Pacific and discussing regime shifts. Thing is - it's not just an El Nino on its own that will cause a permanent jump in surface temperature, it's El Niños in the warm phase of the PDO, combined with greenhouse warming - that precipitate upward shifts in surface temperature.

The inconsistency of deniers

Deniers like to argue that most of the changes we see in global surface temperature are "natural". Yet when Anthony posted this article, he adopted a contrarian view - he complained in his headline that it was "Another excuse for the pause", as if he wasn't happy to find that internal variability can have a significant influence on global mean surface temperature. He did ask the question: “if warming can’t overcome Nature, is it really there at all?”. But all that showed was that he didn't understand what he copied and pasted.

Kevin Trenberth - in depth

If you've 24 minutes to spare, here's a rare longish interview with Dr Trenberth that's well worth watching, from the Denial101x MOOC. You'll get a really good appreciation of weather at the global scale, and how events in one part of the world affect the air, oceans and ice in far distant parts of the world.

From the WUWT comments

Quite a number of people offered Anthony Watts the link to the Science article he asked for, but he didn't take them up on their offer. Otherwise the comments were the lowest common denominator typical of a climate conspiracy blog like WUWT.

Latitude jumped in early to make a non-comment, just wanting his name up there I suppose:

Gunga Din asks a good question. Apart from basic stuff like the greenhouse effect and global warming, there is a lot of unsettled science, as Gavin Schmidt would say. There is still much to learn from science as a whole (and climate science). It's mainly deniers who toss that around as if to say, if we don't know everything there is to know then we don't know anything. Which is pretty dumb, isn't it. What deniers don't know - well that's a whole other thing.

August 13, 2015 at 2:22 pm
*deep breath* Haahaahaahaahaahaahaahaahaa!
Just when I think Trenberth cannot possibly be as oblivious and/or evil as he seems to be, he publishes again!

AndyE didn't bother reading past Anthony's headline. He missed the part about ENSO, and the Pacific Decadal Oscillation and greenhouse warming - in fact he missed everything in his rush to get his name and silly thought in black and white on the one and only WUWT.

August 13, 2015 at 2:36 pm
…….but if Trenberth can’t define the internal, natural variations he, eo ipso, cannot know whether there is any human-caused warming. He should go back to university and do a course in logic.

August 13, 2015 at 2:41 pm
What pause? I though Zeke told us that the new fake temperatures said the pause did not exist.
Meanwhile back in the real world, why do these fraudsters not tell us the AMO is still in the warm phase and when it turns the NH will experience 30 yrs of colder climate?

ristvan is another climate crank who thinks he knows more than the experts. He doesn't, as this comment illustrates so well. Dr Trenberth talks about warm and cool phases of the PDO. They both affect the global mean surface temperature. Without greenhouse warming, they'd even out over time. But they don't - and that's down to us adding CO2 to the air. The world just keeps getting hotter. In the next cool PDO phase, the world will be warmer than it was in the last warm PDO phase - and on it will go until we do something to stop it.

August 13, 2015 at 2:42 pm
Read Trenberth’s comment in Science. RickA link. He trashes Karl, then goes with his ocean heat thing, and predicts the positive PDO will start the warming again. Never occurs to him that part of the 1975-2000 rise might have been natural also. He embraces natural cooling, but not natural warming. Utterly illogical. The desperation amongst the warmunists continues to mount. Their consensus facade is visibly cracking.

You'd think these long term deniers would have known about what Dr Trenberth was saying. Most of them have been protesting climate science for years. It's not anything new. It's been written about before. He's just synthesising known science. Deniers have very short memories - if they have any at all. Joel Snider wrote:

August 13, 2015 at 3:02 pm
Chris Mooney is already pushing this one over at WAPO (and I’m sure the rest of the coordinated media will be following dutifully) because, apparently, this – the 70th or so excuse for the Pause (I’ve lost track, but they tend to volley back and forth between ‘it never happened at all’ and the ‘rationalization/excuse of the week’ for why it did) – but THIS is the one that’s going to away our favorite ‘talking point’.
But I’ll bet… I’ll just bet… there will be another excuse before the end of next week.

NOAA: No pause in the global surface temperature - HotWhopper article describing the above paper - with references and further reading

Houghton, John T. Climate change 1995: The science of climate change: contribution of working group I to the second assessment report of the Intergovernmental Panel on Climate Change. Cambridge University Press.

In the figure above, Kevin Trenberth was using NOAA data, John, downloaded on 30 June 2015 - so after ERSSTv4 was used. (That is, after Kar15). I got that from his paper in Science mag.

It's an unfortunate use of the term - Stefan Lewandowsky's "seepage". I'd say he deliberately used it to make a point.

There was undeniably a slowdown in the ongoing rise in global mean surface temperature these past few years compared to periods when it was rising very quickly. The point that Dr Trenberth is making is that surface temperature doesn't rise at the same rate all the time. He attributes most of the variability to what's happening in the oceans, particularly the Pacific Ocean. (He's showing that when surface temperature rises more slowly for a bit, it doesn't mean that global warming has stopped. Before long it will rise more quickly again.)

Sometimes surface temperature rises faster and sometimes it rises more slowly. Sometimes more heat goes into the ocean and sometimes into the air.

In the video he suggests that sea level is a better indicator of global warming. It's fairly relentless. (Except every now and then a lot of water comes out of the ocean and gets dumped on land, like in the "big wet" of 2011.)

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All you need to know about WUWT

WUWT insider Willis Eschenbach tells you all you need to know about Anthony Watts and his blog, WattsUpWithThat (WUWT). As part of his scathing commentary, Wondering Willis accuses Anthony Watts of being clueless about the blog articles he posts. To paraphrase:

Even if Anthony had a year to analyze and dissect each piece...(he couldn't tell if it would)... stand the harsh light of public exposure.

Definition of Denier (Oxford): A person who denies something, especially someone who refuses to admit the truth of a concept or proposition that is supported by the majority of scientific or historical evidence.
‘a prominent denier of global warming’
‘a climate change denier’

Alternative definition: A former French coin, equal to one twelfth of a Sou, which was withdrawn in the 19th century. Oxford. (The denier has since resurfaced with reduced value.)